Hydraulic brake system for crane hoist drum

Abstract

A hydraulic brake system for the hoist drum of a lifting crane to achieve good control over loads being held or lowered by the load line wrapped on the hoist drum comprises a brake band for exerting a braking force on the hoist drum. The system further comprises a brake cylinder for operating the brake band; a brake valve for controlling the supply of fluid from a fluid source to the brake cylinder; a brake pedal for operating the brake valve and movable between a brake release position and a brake applied position; a valve toggle linkage connected between the foot pedal and the brake valve piston to cause the brake valve to supply fluid to the brake cylinder at a predetermined pressure when the pedal is depressed to a first brake applied position and for applying fluid at a greater pressure when said pedal is moved to a second brake applied position which offers a mechanical advantage; and a hydraulic simulator for adjusting the position to which the foot pedal can be depressed. The hydraulic simulator includes a cylinder, a piston, a biasing spring for biasing the piston to a position wherein all fluid is expelled from the cylinder, and an adjustable stop screw for limiting piston travel, the stop screw being adjustable to control the amount of fluid that can be supplied from the brake valve to the hydraulic simulator when the pedal is depressed to thereby control the extent to which said pedal can be depressed.

I claim: 
     
       1. In a hydraulic brake system for the hoist drum of a lifting crane having an operator's station having a floor, in combination: a hoist drum shaft to be braked;   a brake band for exerting a braking force on said hoist drum shaft;   a brake cylinder operatively connected to said brake band, said brake cylinder comprising a cylinder and piston defining a chamber for accommodating brake fluid therein;   a brake valve located near said floor of said operator's station for controlling the supply of fluid to said brake cylinder, said brake valve comprising a cylinder and a piston defining a chamber for accommodating brake fluid therein;   a source of fluid;   means for supplying fluid from said source to said chamber in said brake valve;   a supply line for supplying fluid from said brake valve chamber to said brake cylinder chamber;   a branch line having one end connected to said supply line and having its other end near said operator's station;   a brake pedal mounted near said floor of said operator's station and movable between a brake release position and a brake applied position;   a valve toggle linkage connected between said foot pedal and said piston of said brake valve, said valve toggle linkage causing said brake valve to supply fluid at a predetermined pressure when said pedal is moved to a first brake applied position and a greater pressure when said pedal is moved to a second brake applied position;   and a hydraulic simulator located near said operator's station for adjusting the position to which said foot pedal can be moved when depressed, said hydraulic simulator comprising a cylinder, a piston slideable in said cylinder and cooperating therewith to define a fluid receiving chamber, said fluid receiving chamber being connected to said other end of said branch line, biasing means for biasing said piston to a position wherein all fluid is expelled from said fluid receiving chamber, a manually adjustable stop means for limiting the travel of said piston, said stop means being manually adjustable to limit the amount of fluid that can be supplied from said brake valve to said hydraulic simulator when said pedal is depressed to thereby control the extent to which said pedal can be depressed said hydraulic simulator further comprising a hollow housing having a pair of end walls spaced apart axially along an axis through said housing, each of said end walls having an opening therethrough along said axis, wherein said cylinder is mounted in the opening in one of said end walls and along said axis, said cylinder having openings at its opposite ends, one of said openings being threaded for receiving said other end of said branch line, wherein said piston is slideable in said cylinder along said axis and has a portion extending into said housing,   wherein said manually adjustable stop means has a threaded portion which threadedly engages threads in said opening in the other of said end walls, said stop means extending into said housing and being engagable with said piston,   wherein said biasing means is disposed between said other end wall and said piston,   and wherein said fluid receiving chamber communicated directly with said threaded opening in said cylinder.   
     
     
       2. A brake system according to claim 1 wherein said brake pedal is pivotally mounted for movement about a first pivot pin; wherein said piston of said brake valve is provided a piston rod having a pivot pin;   and wherein said valve toggle linkage comprises:   a first link having one end pivotally connected to said pivot pin on said piston rod;   a second link which has its lower end pivotably connected by means of a lower pivot pin to a support bracket near said operator's station and which has its upper end pivotably connected by means of an upper pivot pin to the other end of said first link;   and a third link having one end which is connected by means of a second pivot pin to said brake pedal and having another end which is connected by means of a pivot pin to said second link at a point intermediate said upper and lower pivot pins, said intermediate point and said first pivot pin of said brake pedal defining an overcenter line, whereby, as said second pivot pin on said brake pedal moves closer to said overcenter line, the mechanical advantage increases.   
     
     
       3. In a hydraulic brake system for the hoist drum of a lifting crane having an operator's station having a floor, in combination: a hoist drum shaft to be braked;   a brake band for exerting a braking force on said hoist drum shaft;   a brake cylinder operatively connected to said brake band, said brake cylinder comprising a cylinder and piston defining a chamber for accommodating brake fluid therein;   a brake valve located near said floor of said operator's station for controlling the supply of fluid to said brake cylinder, said brake valve comprising a cylinder and a piston defining a chamber for accommodating brake fluid therein, said piston having a piston rod with a pivot pin thereon;   a source of fluid;   means for supplying fluid from said source to said chamber in said brake valve;   a supply line for supplying fluid from said brake valve chamber to said brake cylinder chamber;   a branch line having one end connected to said supply line and having its other end near said operator's station, said other end being threaded;   a brake pedal mounted near said floor of said operator's station and movable about a first pivot pin between a brake release position and a brake applied position;   a valve toggle linkage connected between said foot pedal and said piston of said brake valve, said valve toggle linkage causing said brake valve to supply fluid at a predetermined pressure when said pedal is moved to a first brake applied position and at a greater pressure when said pedal is moved to a second brake applied position, said valve toggle linkage comprising a first link having one end pivotally connected to said pivot pin on said piston rod;   a second link which has its lower end pivotably connected by means of a lower pivot pin to a support bracket near said operator's station and which has its upper end pivotably connected by means of an upper pivot pin to the other end of said first link;   and a third link having one end which is connected by means of a second pivot pin to said brake pedal and having another end which is connected by means of a pivot pin to said second link at a point intermediate said upper and lower pivot pins, said intermediate point and said first pivot pin of said brake pedal defining an overcenter line, whereby, as said second pivot pin on said brake pedal moves closer to said overcenter line, the mechanical advantage increases;   and a hydraulic simulator located near said operator's station for adjusting the position to which said foot pedal can be moved when depressed, said hydraulic simulator comprising a hollow housing having a pair of end walls spaced apart axially along an axis through said housing, each of said end walls having an opening therethrough along said axis, a cylinder mounted in the opening in one of said end walls and along said axis, said cylinder having openings at its opposite ends, one of said openings being threaded for receiving said other end of said branch line, a piston slideable in said cylinder and cooperating therewith to define a fluid receiving chamber, said fluid receiving chamber being connected to said other end of said branch line through said threaded opening, said piston being slideable in said cylinder along said axis and having a portion extending into said housing, biasing means disposed between said other end wall and said piston for biasing said piston to a position wherein all fluid is expelled from said fluid receiving chamber, and a manually adjustable stop means for limiting the travel of said piston, said stop means being manually adjustable to limit the amount of fluid that can be supplied from said brake valve to said hydraulic simulator when said pedal is depressed to thereby control the extent to which said pedal can be depressed, said manually adjustable stop means having a threaded portion which threadedly engages threads in said opening in the other of said end walls, said stop means extending into said housing and being engagable with said piston.